1. Field of the Invention
This invention relates to an apparatus and method for causing vortices in test tube samples, and more specifically, to an apparatus and method for selectively and automatically causing vortices in a test tube and adding and removing samples therefrom.
2. Background Description
Frequently laboratory samples have to be mixed as part of a test procedure so that the portion of the sample tested or analyzed is representative of the entire specimen. A variety of test equipment available to mix or shake test samples directly stirs the test sample in its container or shakes the container and sample. Stirring devices usually include a member which is placed into the sample within the container to spin the sample about the axis of the member. Typically the member has to be cleaned after use and the container is subject to the stresses imposed by contact with the member during stirring.
The most commonly used laboratory sample mixing equipment is designed to shake the container and its contents to eliminate the need to clean a mixing or stirring member. Shaking the container and the contents works well for messy materials including paints and lubricants. Similarly, dangerous substances such as acids and other active chemicals are mixed within the container thus eliminating concern about destruction of, or contact with the stirring member.
Biohazardous substances are frequently tested for deadly cancers, virus, infection or the like and thus typically require particular care during handling. Consequently, laboratory mixing and stirring equipment which does not include a member that contacts the hazardous specimens is safer to use than stirring members which have to be handled. Another form of mixer includes a flat shaker table upon which the sample container is placed. Often the laboratory vessel has a flat bottom which can be placed upon the vibrating table that moves in a plane in two directions imparting orbital motion to the container and sample. The orbital motion agitates the sample. Problems with handling and cleaning flat bottomed vessels remain a concern even though vibrating tables are inexpensive to make and use. Vibrating tables are not suited for use with test tubes. Samples are usually in a test tubes with spherically shaped bottoms that are inexpensive and disposable or are easy to clean and reuse.
Shakers can be used for mixing the contents of one container with several test tubes. The individual handling of test tubes is slow and automated handling presents the difficulty of being unable to have equal incubation times for all the samples. Specifically, as the samples are prepared one at a time in each test tube prior to mixing as a group, delays occure resulting in some of the samples incubating longer than others.
Various test tube shaking, rotating and revolving devices have been developed and used for mixing the contents of a plurality of test tubes. One device holds a number of test tubes in a rack designed to individually support each test tube near the longitudinal middle of each tube so that the rack and tubes can be swung about the midpoint of the axes of the tubes to mix the samples sealed within the tubes. The problem with swinging racks of sealed test tubes is handling since each tube has to be sealed and placed in the rack. A variation of such swinging rack mixers merely swings the tube through a small arc to agitate the contents without spillage even though the tubes are unsealed.
Vortex causing mixers are frequently used to mix the contents of individual test tubes by placing the rounded bottom end of a single tube into a rubber pocket which has a switch activated by pressing the test tube into the pocket. Closing the switch makes the vortex causing mixer orbit the rounded test tube bottom about the longitudinal axis of the test tube. The top of the test tube is hand held in substantially one place such that the lower end of the test tube orbits establishing a vortex in the sample. Motion of the test tube is designed to cause a vortex in the sample due to the eccentrically orbiting resilient pocket into which the bottom of the test tube is manually placed while the top of the test tube is held stationary by a laboratory technician. The technician must control the mixing by varying the angle of contact and pressure on the drive cup during mixing. One such manually operated mixer is the VWR Vortex Mixer manufactured by Scientific Industries, Inc. of Bohemia, N.Y., as disclosed in U.S. Pat. No. 3,061,780. Each test tube and sample must be individually placed in the pocket so samples can be individually caused to vortex.
Certain analytical equipment is designed to handle a plurality of samples carried in special racks from which the samples can be accessed automatically. Such analytical equipment requires that the samples be mixed in order to provide a homogenous or representative portion of the specimen to be tested. Automatic accessing of the samples from each test tube means that each tube with a well mixed sample has to be held in a rack which positions each tube for access such a rack does not provide for automatic mixing. Presently available test tube racks or mixing equipment are not designed to minimize handling by the technician during mixing or to cooperate with analytical equipment.